Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $187.73   8.714%   $204.0888   $204.09   $204.10   $204.10  
  Purchase #2 $80.57   3.270%   $83.2046   $83.20   $83.20   $83.20  
  Purchase #3 $86.61   10.126%   $95.3801   $95.38   $95.40   $95.40  
  Purchase #4 $114.70   9.381%   $125.46   $125.46   $125.45   $125.50  
  Purchase #5 $61.41   12.550%   $69.117   $69.12   $69.10   $69.10  
  Purchase #6 $202.71   11.392%   $225.8027   $225.80   $225.80   $225.80  
  Purchase #7 $14.84   8.120%   $16.045   $16.05   $16.05   $16.00  
  7 purchase totals = $748.57       $819.0982   $819.10   $819.10   $819.10